26-29
Of course, that is if it's by choice. I think most women in relationships (or married) are ready in their mid-to-late 20s (financially, emotionally, physically). I wouldn't want to have children into my 30s and I, personally, want to be done by 33 or 34. I want to be young enough so my body can bounce back from the pregnancy, but old enough for the huge responsibility.
But, if I got pregnant now, at almost 23, I think I would be ready (for the most part) and I would be happy, not disappointed. For now, I assume I'll get married around 25, so I will probably starting having children around 28. Seems like a good age to me.